Resolution Criteria

This market resolves YES if there are at least five confirmed cases of polio (either wild poliovirus or vaccine-derived poliovirus) in the United States during the 2025 calendar year.

Background

The United States has been officially polio-free since 1979, when the last case of wild poliovirus was reported. However, in recent years, there have been concerning developments:

• In 2022, a case of vaccine-derived poliovirus was identified in New York state, and subsequent wastewater surveillance detected poliovirus in multiple counties

• Vaccination rates have declined in some communities, creating potential vulnerability to outbreaks

• Globally, polio remains endemic in Afghanistan and Pakistan, with recent outbreaks in countries like Malawi and Mozambique

Considerations

• The U.S. primarily uses inactivated poliovirus vaccine (IPV), which prevents disease but doesn't stop transmission as effectively as the oral vaccine

• CDC and public health authorities maintain surveillance systems to detect poliovirus in wastewater and clinical samples

• For context, a comeback of five or more cases would represent a significant public health event, as the U.S. has averaged zero indigenous cases for over four decades